Radio teletype system



March 22, 1949. F. J. wER/THMANN ET AL. 2,464,837

RADIO TELETYPE SYSTEM V ffm/*mam* wmf/funzia MMQM? ATTRNEY March 22,1 1949. F, J. WERTHMANN ET AL 2,464,837

` RADIO TELETYPE SYSTEM Filed Maya, 194e 4 sheets-sheet 2 HHH/mfg y WinMx/mfg @van Kc fa 42 7/ WM-ANH A TTOR/VEY March 22, 1949- I F. J. WERTHMANN ET AL 2,464,837

RADIO TELETYPE SYSTEM Filed May 2,1946 4 sheets-sheet 5 we @ff/au,

' ArroR/vEr March 22, 1949. F. J. WERTHMANN ET AL 2,454,837

RADIO TELETYPE SYSTEM r1 r Lili A from/5r Patented Mar. 22, 1949 RADIO TELETYPE SYSTEM Florian J. Werthmann and Gleneth F. Collar, Seattle, Wash., and Reinhold vF. Blomquist,

Rushville, Nebr.

Application May 2, 1946, Serial No. 666,778

3 Claims. (Cl. 178-61) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

Our invention is concerned with the art of duplex telegraphy and is a system for simultaneous transmission of two teletype signals over a single channel by means of a signal in which the intelligence is conveyed by frequency changes which are permutations among four frequencies. This system has the advantages that the transmitted signal operates at all times at maximum energy, that the signal occupies a minimum of band width, and that interfering noises have no tendency to cause false signals. No synchronizing means are required. The transmitted signal at any instant is a continuous wave of xed frequency.

It is one object of our invention to provide a system for simultaneous transmission of two teletype code signals over a single channel.

It is another object of our invention to provide a system for simultaneous transmission of two mark-space code signals over a single channel with constant signal energy and minimum band width.

It is another object of our invention to provide 4a system by which a one-to-one correspondence is set up between the four possible combinations of signal of two superposed mark-space codes and a selection one at a time from a group of four frequencies, as will appear more fully hereinafter.

It is another object of our invention to provide a. duplexing system for teletype code not requiring synchronizing means between transmitter and receiver. 1'

Our invention will be better understood by reference to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings,

Figure 1 is a block diagram of a transmitting portion of a complete system embodying our invention.v

Figure 2 is a block diagram of a receiving portion. of a complete system embodying our invention.

Figure 3 is a circuit diagram of the duplexer part of the transmitting system.

Figure 4 is a circuit diagram of part of the duplexer of the ltransfhitting system.

It is well known in the prior art to prepare on i `one teletypewriter a mark-space code signal representing the various characters and spaces of a typewritten message and to receive this signal on a second teletypewriter whereon the message is automatically typed. As constructed, each typewriter comprises both transmitting and receiving components. The output of each teletypewriter transmitter is a direct current of constant amplitude coded in marks and spaces. The in; put to each teletypewriter receiver is direct current, the marks being represented by current in one -coil of a relay, the spaces by current in an oppositely acting coil of the relay.

The general method employed in our invention is to set up a correspondence between the various combinations of mark and space which are obtained by combining two mark-space signals and a selection of one frequency from a group of four frequencies.

The possible mark-space combinations and the correlated frequencies are listed below. The correlated frequencies have been denominated by letters, as well as given suitable Values. The values are selected to have no simple harmonic interrelation, and so as to be separable in frequency selective filters.

Correlated frequency Code combination 1 F, 2000 cycles Teletypewriter A on mark Teletypewriter B on markl code combination 2 G, 1700 cycles.

Teletypewriter A Teletypewriter B mal Space code Combination 3 H, 1400 cycles Teletypewriter A Teletypewriter B Space Space Code combination 4 K, 1100 vcycles Teletypewriter A on space Teletypewriter B on mark in the form of direct voltage for the marks and absence of voltage for the spaces. These signals are combined in duplexer I. The virtual equivalents of the four corresponding signal tones above referred to are formed in duplexer I and passed to radio transmitter 2, from which they are radiated. It is within the scope of our invention to transmit the four frequencies as four modulations in various orders of succession on a constant carrier. However, in the interest of compressing the band Width used in transmission we prefer effectively to suppress the carrier and the lower side bands and transmit the upperl side bands only. This physically consists in transmitting in successive permutations four continuous wave signals close together in frequency. For a virtual suppressed carrier of 5,000 kc. the actual frequencies of continuous wave transmission may have the values 5002.0 kc., 5001.7 5001.4 kc. and 5001.1 kc., to supply upper side bands corresponding to the virtual modulations of 2000, 1700, 1400 and 1100 cycles.v

In Figure 2 is shown a receiver 3 for receiving the signals transmitted from transmitter 2. The virtual suppressed carrier of 5000 kc. is supplied at the input to receiver 3 from a local beat frequency oscillator 4. Beats between locally supplied carrier and the received side bands are then formed in receiver 3, and its audio output consists of the difference beat frequencies 2000, 1700, 1400 and 1100 cycles, so that the signals of frequencies F, G, H, and K correlated with the teletypewriter mark-space combinations at the transmitter are created in the receiver and in the sequence of the combinations.

From the receiver the audio signals are passed through a noise lter 5 designed to pass the band 1100 to 2000 cycles and suppress other frequencies, thence through a limiter 6 which cuts the signals down to a fixed amplitude and through a bank of four frequency selective lters 1 to I0 designed to isolate the four signals. The four filters 1, 8, 9 and I0 are tuned respectively to thefour frequencies F, G, H and K.

The outputs of the filters are then recombined by pairs in tone mixer II; that is, for signal output from either filter 1 or 8 a direct-current "mar signal is passed to the teletypewriter receiver C over lead I4. For signal output from filters 8 or 9 a direct-current space signal is passed to teletypewriter receiver D over lead I5. Similarly for signal from either filters 9 or I0 a space signal passes to teletypewriter receiver C over lead I2, and for signal from either nlters III or 1 a mark signal passes to teletypewriter receiver D over lead I3.

Thus the code signal from the teletypewriter transmitter A is applied to teletypewriter C and simultaneously the code signal from teletypewriter B is applied to teletypewriter D.

In Figure 3 is shown a preferred form of duplexer. It comprises essentially a bank of keying tubes I6, I1, I8 and I9, and a bank of keyed tubes 20, 2i, 22 and 23.

Keying tubes I6, I1, have load resistors 24,

minal connected to the negative terminal of negative bias supply 30 and its positive terminal connected to the tongue of a single-pole doublethrow relay 38. One xed contact of relay 33 is connected to the grid of tube I6, the other to the grid of tube I1. Relay 38 is controlled 'oy the mark-space signal from teletypewriter A to which its coil is connected, the control being in the sense that positive bias 36 is connected to the grid of tube I1 (and disconnected from the grid of tube I6) for a mark signal and connected to the grid of tube I6 (and disconnected from the grid of tube I1)v for a space signal.

In entirely analogous manner the plates of keying tubes I8 and I9 are connected respectively through load resistors 26 and 21 to a common plate voltage supply 29 having its positive terminal grounded. Grids of tubes I8 and i9 are connected respectively through resistors 34 and 35 to negative bias supply 3|, the positive terminal of which is connected to the common junction of the cathode of tubes I8 and I9 and the negative terminal of plate voltage supply 20.

In series with negative bias supply 3i is a positive bias supply 31' having its negative terminal connected to the negative terminal of negative bias supply 3l and its positive terminal connected to the tongue of a single-pole doublethrow relay 39. One xed contact of relay 39 is connected to the grid of tube I8, the other to the grid of tube I3. Relay 39 is controlled by the mark-space signal from teletypewriter B, to which its coil is connected, the contact being in the sense that positive bias 31 is connected to the grid of tube I9 (and disconnected from the grid of tube I8) for a mark signal and connected to the grid of tube I8 (and disconnected from the grid of tube I9) for a space signal.

Eight equal dropping resistors 40-41 are connected in series in a loop, as is shown quite plainly in Figure 4. The junction of resistors 40 to 4I is connected through limiting resistor 48 to the grid of keyed tube 20. In similar fashion the junction of resistors 42 and 43 is connected through limiting resistor 49 to the grid of keyed tube 2|, junction of resistors 44 .and 45 through resistor 50 to grid of tube 22, junction of resistors 46 and 41 through resistor 5I to grid of tube 23. The junction of resistors 41 and 40 is connected directly to plate of tube I 6, of resistors 4I and 42 to plate of tube I8, of resistors 43 and 44 to plate of tube I1, of resistors 45 and 46 to plate of tube I9.

An oscillator 52 having a frequency of carrier plus frequency F, that is to say, 5002.0 kc., feeds its output into the grid cathode circuit of keyed tube 20 through resistor 48. Similarly an oscillator 53 having a frequency of carrier plus frequency G, that is, 5001.7 kc., feeds the grid of tube 2I through resistor 49; an oscillator 54 having a frequency of carrier plus frequency H, hence 5001.4 kc., is connected to the grid of tube 22 through resistor 50, and an oscillator 55 4having a frequency of carrier plus frequency K, or 5001.1 kc., applies its output to the grid of tube 23 through resistor 5I.

The plates of keyed tubes 20, 2|, 22, 23 are tied together and receive their plate voltage through the primary of a radio frequency transformer 56. 'I'he secondary of transformer 56 feeds signal to transmitter 2 for transmission.

' In operation `a mark signal from teletypewriter A pulls down the tongue of relay 3,8. putting positive bias on the grid of tube I 71 `and hence negative bias on the grid of tube I6. Tube rI6 draws y no current and its plate is at ground potential. Tube I1 draws current and its plate falls below ground potential. A simultaneous mark signal from teletypewriter B puts the plate of tube I8 at ground potential and the plate of tube I9 below ground potential. By reference to Figure 4 it is seen that this operation grounds the junction of resistors 46 and 4I and puts at negative potential the junctions of resistors I2 and 43, 44 and 45, and 46 and 41. Thus the grid of keyed tube 20 is biased to ground, permitting signal from oscillator 52 to pass through tube 20 to transformer 56. The grids of keyed tubes 2|, 22, 23 are all biased so negatively that no signal is allowed to pass from oscillators 53, 54 and 55 to transformer 56.

It will be seen that any combination of mark and space signals from the two teletypewriters A and B results in signal being passed from one of the four oscillators and blocked from the other three. It will be seen further that the frequency of signal which is passed is carrier frequency plus the audio frequency correlated with the concomitant code combination as set up in the table above.

The tuning of transmitter 2 is broad enough to transmit all four frequencies without retuning.

It is seen that duplexer I has converted the code combinations from the two teletypewriters into a corresponding spectrum of four frequencies.

At the receiver station an inverse operation is effected in order to separate the two coded signals. A preferred circuit for accomplishing this result is shown in Figure 5, this circuit constituting the tone mixer I I.

Tone mixer II comprises four double triode tubes 64, 65, 66 and 61. The double grids of tube 64 are fed from a common input terminal 60, similarly the double grids of tube 65 are fed from terminal 6I, those of tube 66 from terminal 62, and those of tube 61 from terminal 63. One plate of tube 64 is connected through primary of audio transformer 66 to one plate of tube 65. The other plate of tube 65 is connected through primary of transformer 69 to one plate of tube 66. Similarly plates of tubes 66 and 61 are connected through primary of transformer 10 and plates of tubes 61 and 64 through primary of transformer 1I. The centers of these transformers, grounded for audio frequencies, are connected to the positive terminal of a common plate voltage supply.

The secondaries of transformer 68, 69, 10, 1I are connected respectively to rectiers 12, 13, 14, 15.

Output of rectiiier 12 is conducted through lead l2 to the space control coil 18 of teletypewriter receiver C. Similarly, output of rectier 13 is conducted by lead I3 to mark control coil 19 of teletypewriter D; output of rectifier 14 is conducted by lead I4 to mark control coil 16 of teletypewriter C; output of rectifier is conducted by lead I5 to space control coil 11 of teletypewriter D.

The four frequencies F, G, H and K are received from tone iilters 1, 8, 9 and I 0 at terminals 62, 63, 60 and 6I, respectively. Responsive to signal H tube 64 passes signals to both transformers 1I and 68 and thence to rectiers 12 and 15, respectively, wherein the audio-frequency signals are converted into direct-current signals. Similarly tube 65 responsive to signal K passes signals to both transformers 68 and 69, which are rectied in rectiers 12 and 13. Thus a directcurrent control signal v appears inI the output of rectier 12 responsiye to either H or K signals but to no others., Hence the` output of the rectifier 12 produces the space signal of teletypewriter A and this signal is applied through lead I2 to the space control coil 18 of teletypewriter receiver C, so that teletypewriter C reproduces the space signal initiated at teletypewriter A. Similarly bothv signals F and G produce signal in rectier 14 and in mark control coil 16 of teletypewriter receiver C; so that teletypewriter C reproducesl the code of teletypewriter A.

Similarly, signal appears at rectier 13 responsive both to signals K and F applied to terminals 6I and 62, respectively. Accordingly the output of rectifier 13 reproduces the mark signal of teletypewriter transmitter B and this signal is applied through a lead I3 to the space control coil 19 of teletypewriter receiver D. Accordingly there is reproduced in teletypewriter D the mark signal of teletypewriter B. Lastly signals G and I-I through rectifier 15 reproduce the space signal of teletypewriter B in coil 11 of teletypewriter D. Thus teletypewriter D reproduces the message of teletypewriter B just as teletypewriter C reproduces the message of teletypewriter A.

Having described one embodiment of our invention we wish it understood that the invention is not to be limited to the particular embodiment described but only by the appended claims.

What we claim and desire to protect by Letters Patent is:

1. A dupleXer comprising, a loop of eight serially connected impedances having a first set oi four alternate junctions and a second set of four alternate junctions, four keying means connected respectively to each of the four junctions of said iirst set whereby the potential at each of 'these four junctions may be keyed between ground and a negative direct potential, and four sources of alternating potential together with four bias-responsive means connected respectively to the :four junctions of said second set whereby each said bias-responsive means passes alternating potential from said source therewith connected when the junction therewith connected lies between two adjacent junctions of said rst set which are at ground potential but blocks passage of alternating potential from said source therewith connected when the junction therewith connected lies adjacent to a junction of said first set which is at negative potential.

2. In a duplexing system, four primary "on-a Y keying means arranged as in analogy to the corners of a square with opposite pairs of said keying means being oppositely on and 01T, four secondary on-orf keying means arranged as in analogy to sides of said square and responsive to said four primary keying means, and means for setting at on only that one of said secondary keying means which is positioned on that side which lies between the two corners at which the said primary keying means are set at oni 3. In a receiver for a duplexed code signal having the character of four components of different frequencies in permutation, frequency selective means for isolating the components of the signal in four separate channels, respectively designated A, B, C, D, and means connecting channels A and B at their output terminals unilaterally to a rst rectifier, means connecting channels C and D at their output terminals unilaterally to a second rectifier, relay means responsive to said rst and second rectiiiers acting in mutual opposition,

REFERENCES CITED The following references are of record in the le of this patent:

Number UNITED STATES PATENTS Name Date Barclay May 5, 1903 Mathes June 14, 1927 Robinson Mar. 6, 1928 Ilberg Nov. l, 1932 Cox Nov. 10, 1942 Bumstead July 23, 1946 

